Why do you think companies or people need PR when effective sales/marketing strategies are there to do better than PR?

Strategies and a marketing design work well only when complemented by PR. It's the face to the brain that has been working behind the scenes. The people aspect of PR, its ability to tackle tricky media situations, handling investors, ensuring company credibility infront of its customers and business clients is soley a PR forte. :)

Public Relations can be an activities that build awareness and credibility for a company, product or service through other or third party - influencers - media, bloggers etc. So it is others describing about the products.

Marketing works to communicate the value offerings to customers, potential clients, employees and investors through advertising, newspapers, websites etc. So its a self description.

Sales is essentially the act of closing the leads brought in by your marketing and public relations efforts

PR includes reputation management - how to deal positively with a crisis.

PR builds more creditbility for the brand or product.

Customers are trust to third party thru PR than promoting the product thru advertising or marketing.

Hence PR is playing a vital role in promoting the products and integration of the above three are most effective for the company product or the business.

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Sales & Marketing division has to do with the product/service sales rather PR has to mange many things under their head. PR has to be bridge link between company and customer. Only good PR can win the customer even if your product is not upto the mark. 

PR can solve many grievance issues where sales & marketing division can not enter. It help in making brand more solid.

Put it this way, marketing,sales and customer service is a company's24/7 PR team.

The other PR team is there only for press release season.